Space and astronomy

Astronomy is the study of everything beyond the Earth's atmosphere, from the nearby Moon and planets to the most distant galaxies. The objects it covers span an enormous range of scale. Closest to home is the solar system, in which the Sun is orbited by eight planets, their moons, and smaller bodies such as asteroids, comets and dwarf planets like Pluto. Beyond the solar system lie the stars, vast nuclear furnaces of which the Sun is an ordinary example, gathered together into galaxies such as our own Milky Way.

On the largest scale, cosmology studies the universe as a whole: its contents, structure and history. The prevailing scientific account is the Big Bang model, in which the universe began in an extremely hot, dense state and has been expanding and cooling ever since. Evidence for this includes the observed expansion of the universe, in which distant galaxies recede from us, and a faint background of microwave radiation left over from the early universe. Among the most extreme objects astronomers study are black holes, regions where gravity is so strong that not even light can escape.

Much of what is known about space comes from telescopes and spacecraft. Ground-based and orbiting telescopes, such as the Hubble Space Telescope, collect light and other radiation from distant objects, while robotic probes like the Voyager spacecraft have travelled to the outer planets and beyond. Agencies including NASA and the European Space Agency build these instruments and missions, and the images and data they return continue to refine the understanding of planets, stars, galaxies and the origin of the cosmos.

Frequently asked questions

What is the Big Bang?

It is the leading scientific model for the origin of the universe, describing how it began in an extremely hot, dense state and has expanded and cooled over billions of years.

What is a black hole?

A black hole is a region of space where gravity is so strong that nothing, not even light, can escape once it crosses the boundary called the event horizon.

How do astronomers study distant objects?

They use telescopes on the ground and in orbit to collect light and other radiation, and send robotic spacecraft to visit planets and other bodies in the solar system.